This application claims the priority of German application 197 46 602.8, filed in Germany on Oct. 22, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a spinning process in which at least one sliver is opened to single fibers which are deposited on a moving collecting surface and are compressed transversely to their motion of direction to form a strand, the strand being transported through a nipping line and twisted to a yarn downstream of the nipping line under the action of a rotating air stream.
In U.S. Pat. No. 4,676,062 a process of this type is disclosed. A rapidly rotating opening roller opens a sliver to single fibers, which are carried in the form of a so-called fiber swarm by an air current and deposited on a collecting surface of a rotating sieve drum. The air current which transports the fiber swarm to the collecting surface is increasingly confined laterally by means of channel walls, so that the single fibers are deposited on the collecting surface, which has only a narrow suction slit, as an already condensed strand. This strand is transported through a nipping line, which the sieve drum forms together with a nipping roller. A further s-sieve drum may be arranged downstream of the sieve drum before reaching the nipping line, which second sieve drum takes up the condensed strand and which sieve drum can be driven with a higher or a lower speed. Downstream of the nipping line is a twist nozzle (not described in detail), which imparts a false twist to the strand. After the false twist has disentangled again, spread out single fibers are wrapped around the strand and thus form a yarn, whose interior fibers are essentially free of any twist.
The advantage of the known spinning process is to be seen in that during the execution of the known pneumatic false twist spinning, the usually present drafting arrangement is replaced by an opening roller, whereby after the single fibers have been opened from the sliver before reaching the twist nozzle, a strand is formed which is not unlike the sliver coming from a drafting arrangement. What is a disadvantage, however, is that the parallel alignment of the fibers originally present in the sliver is lost when the opened single fibers are transported in an air current, so that the fiber swarm arriving at the collecting surface does not consist any more of orderly deposited fibers. It is further a disadvantage that the formed yarn is twisted only in its outer area by means of wrapping fibers, while the core of the yarn, as is usual in pneumatic false twist spinning, is to a great extent twist-free.
From U.S. Pat. No. 5,775,086 it is known that single fibers, from one or more slivers, opened by means of an opening roller and in the form of a fiber veil, are deposited on a moving collecting surface arranged downstream, which is here also in the form of a sieve drum. The periphery of the opening roller is perforated and suctioned, so that the end of the sliver, the so-called fiber beard, is intensively combed. The collecting surface is in close proximity to the fiber beard and takes up the single fibers before their speed becomes too high. This action is supported by the perforation of the opening roller, which in this embodiment can run relatively slowly. As the teeth of the opening roller have a negative front angle, the transfer of fibers from the opening roller to the collecting surface takes place very quickly. A fiber veil arises, in which the single fibers are arranged parallel to one another and aligned in their direction of motion. The disadvantage to this embodiment is the yarn withdrawal, which runs transverse to the direction of motion of the collecting surface, so that the single fibers arriving at the spinning line are false twisted before a real twist is imparted by a twist device arranged downstream. The formed yarn in this arrangement is thus not sufficiently tear-resistant.
It is known from German published patent application 40 40 102 that single fibers are deposited on a collecting surface in the form of a rotating disc, and are condensed more and more to a strand by pneumatic means, namely a suction slit which tapers in transport direction. The condensed strand is guided to a twist nozzle which, as in the prior art mentioned above, creates a yarn whose fibers located at the yarn core are, to a great extent, twist-free. Due to the omission of a nipping line directly before the twist nozzle, that point which acts as a twist block is not well defined.
A further developed twist nozzle is known from U.S. Pat. No. 5,159,806, which not only false-twists a thread fed from a drafting arrangement, as is usual in pneumatic false twist spinning, but rather furthermore ensures by special means the spreading of fiber ends, which wrap themselves helically around the forming yarn. The twist nozzle comprises in its interior a needle-like guiding element aligned in the direction of motion of the fiber strand, which guiding element is disposed inside the fiber strand and directed towards an entry opening of a yarn withdrawal tube. Thus the fiber strand is spread to such an extent that the fiber ends are spread in sufficient number and sufficient length, so that the forming yarn has an open-end like character. The drafting arrangement arranged upstream is very susceptible and requires much maintenance due to the required high drafting, so that in this process the withdrawal speeds actually possible cannot be utilized to their full extent.
It is an object of the present invention to improve the above named spinning process in that the advantages of the additional described prior art can be used without having to take into account the accompanying disadvantages. In particular, a spinning process is to be devised whereby an open-end like yarn is generated by means of a twist nozzle and using an opening roller, whereby, during the entire spinning process, the originally present parallelism of the single fibers in the sliver is not lost.
This object has been achieved in accordance with the present invention in that
the single fibers, after they have been opened from the sliver, are disposed on the collecting surface in the form of an expanded fiber veil, PA1 the fiber veil is subsequently condensed to the strand and PA1 under the action of a rotating air stream, fiber ends are spread out of the strand.
The fiber veil taken up by the collecting surface consists then of single fibers extending parallel and in the direction of motion, when the transfer does not take place in an air stream inside a fiber channel, but rather when, for example, the collecting surface is located relatively near to an opening roller. The number of single fibers in the fiber veil may already correspond to the number of fibers located in the cross section of the yarn. Due to the condensing of the fiber veil transversely to its direction of motion on the collecting surface, the parallel alignment of the fibers is maintained, and a strand arises, corresponding to a large extent to the proportions of a standard drafting arrangement. A nipping roller, which defines the spinning line, is also a contributory factor. The twist nozzle arranged downstream of the nipping line can in principle correspond to one which, for example, spreads out fiber ends from a strand in sufficient amounts and length by means of a needle-like guidance.
It can be favorable when the strand is stretched in the direction of motion during condensing. This can take place, for example, in that a drafting roller rotating slightly faster is arranged downstream of a transport roller comprising the collecting surface, which drafting roller takes over the already slightly condensed fiber veil and condenses it completely to a strand. The single fibers are hereby accelerated somewhat and improved further in their alignment.